1. Field of the Invention
This invention relates to a method and a system for determining a heating point and a heating line in the bending of a steel plate. More specifically, the invention relates to the method and system useful for application to the bending of a steel plate having complicated curved surfaces, such as an outer panel of a ship hull.
2. Description of the Prior Art
The outer panel of a ship hull is composed of a steel plate about 10 to 30 mm thick with a complicated undevelopable curved surface which reduces propulsion resistance for efficient navigation in the water. To form this curved outer panel, a processing method generally called line heating has been known for long. This method heats the surface of a steel plate locally by means of a gas burner or the like, to cause the extraplane angular deformation or intraplane shrinkage deformation of the steel plate due to plastic distortion, and skillfully combines these deformations to obtain the desired shape. This method is used at many shipyards.
FIG. 1 is an explanation drawing conceptually showing an earlier technology concerned with a method for bending a steel plate to serve as an outer panel of a ship hull. FIG. 2 is a front view showing a wooden pattern for use in the bending in a state in which it is mounted on the steel plate. As shown in both drawings, according to the earlier technology, many (10 in the drawing) wooden patterns 1 following frame lines of the outer panel of the ship hull (lines extending along frame materials for the outer panel at positions where the frame materials are attached; the same will hold in the following description) as target shapes are mounted on a steel plate 2. Then, an operator compares the shapes of each wooden pattern 1 and the steel plate 2 by visual observation, and considers differences between their shapes, e.g., the clearance between the wooden pattern 1 and the steel plate 2. Based on this consideration, the operator studies what position to heat in order to bring the steel plate 2 close to the target shape. As a result, the operator determines each heating position (heating point). Concretely, the wooden pattern 1 is rolled along the frame line of the steel plate 2 in a vertical plane (the same plane as in FIG. 2). The points of contact of the wooden pattern 1 with the steel plate 2 during the rolling motion are watched to determine the heating points in consideration of the clearance between the wooden pattern 1 and the steel plate 2 in each state.
Then, it is considered how to connect the respective heating points together in order to make the steel plate 2 similar to the target shape. Based on this consideration, a heating line is determined. As shown in FIG. 3, heating lines 3 that have been determined are marked on the surface of the steel plate 2 with chalk or the like, and the steel plate 2 is heated with a gas burner along the heating lines 3.
With the earlier technology as described above, the steel plate 2 is heated with a gas burner by the operator along the heating lines 3 determined by the operator""s sense based on many years of experience. As a result, a predetermined curved surface is obtained. Acquiring the ability to determine the heating lines 3 rationally is said to require more than about 5 years of experience. This has posed the problems of the aging and shortage of experienced technicians. The bending procedure also takes a large amount of time for incidental operations, such as the production, mounting and removal of the wooden pattern 1 for the steel plate 2, thus lengthening the entire operating time.
To solve the problem of the shortage of experienced technicians and reduce the operating time, it is necessary to improve, theorize and automate the bending operation while taking into consideration know-how that operators acquired through experience.
The present invention solves the above-described problems with the earlier technologies. The object of this invention is to provide a method and a system for determining a heating point and a heating line in steel plate bending, the method and system being capable of determining the heating point and heating line without using a wooden pattern, and being capable of assisting in the automatic determination of the heating point and heating line.
The invention that attains the foregoing object is characterized by the following aspects:
1) Placing a virtual wooden pattern formed from target shape data on a virtual steel plate formed from steel plate shape measurement data, the target shape data being related to a target shape of a steel plate to be bent, and the steel plate shape measurement data being obtained by measuring a surface shape of the steel plate; rolling the wooden pattern or steel plate along a specific line on the steel plate, such as a frame line, from a predetermined reference position in a plane including a cross section of the steel plate, to bring the wooden pattern and the steel plate into contact at two points, with the contact points on the steel plate being designated as A, B, and the contact points on the wooden pattern being designated as C, D; then rolling the wooden pattern or the steel plate in the reverse direction to return it to the reference position; with the wooden pattern or the steel plate being returned to the reference position, obtaining a straight line U connecting the contact points A, B and a straight line V connecting the contact points C, D; and determining a heating point on the basis of a point of intersection of the straight lines U, V, and also determining a bending angle for the steel plate at the heating point on the basis of an angle of intersection of the straight lines U, V;
after obtaining a heating point, or a heating point and a bending angle, relative to a certain reference point, repeating the same steps as described above while bringing the contact points A, C on a reference point side, which have been used in the determination of the heating point, into contact with each other to use their contact point as a new reference point, thereby determining respective heating points, or respective heating points and respective bending angles, along a specific line up to the end of the steel plate;
drawing straight lines from a certain heating point on a certain line, as a starting point, to heating points on other lines on the basis of the heating points that have been determined in this manner; examining the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if the degree of parallelism is within a predetermined range, performing grouping of the relevant heating points as the heating points of the same group; and connecting the respective heating points of the same group by a straight line or a curve to determine a heating line; or
drawing straight lines from a certain heating point on a certain line, as a starting point, to heating points on other lines on the basis of the heating points that have been determined; examining the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if this degree of parallelism is within a predetermined range, performing grouping of the relevant heating points as the heating points of the same group; and connecting the respective heating points of the same group by a straight line or a curve to determine a heating line, and also imparting as data the amounts of heating at the respective heating points that have been determined on the basis of the bending angles of the steel plate at the respective heating points; or
drawing straight lines from a certain heating point on ascertain line, as a starting point, to heating points on other lines on the basis of the heating points that have been determined; examining the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if this degree of parallelism is within a predetermined range, and if the amounts of heating at the heating points determined by the bending angles of the steel plate at the respective heating points are equal to each other, performing grouping of the relevant heating points as the heating points of the same group; and connecting the respective heating points of the same group by a straight line or a curve to determine a heating line.
2) Having a heating point determining unit which reads in target shape data on a target shape of a steel plate to be bent, and steel plate shape measurement data obtained by measuring a surface shape of the steel plate; places a virtual wooden pattern formed from the target shape data on a virtual steel plate formed from the steel plate shape measurement data; rolls the wooden pattern or steel plate along a specific line on the steel plate, such as a frame line, from a predetermined reference position in a plane including a cross section of the steel plate, to bring the wooden pattern and the steel plate into contact at two points, with the contact points on the steel plate being designated as A, B, and the contact points on the wooden pattern being designated as C, D; then rolls the wooden pattern or the steel plate in the reverse direction to return it to the reference position; with the wooden pattern or the steel plate being returned to the reference position, obtains a straight line U connecting the contact points A, B and a straight line V connecting the contact points C, D; calculates the three-dimensional coordinates of a heating point on the basis of a point of intersection of the straight lines U, V, and also calculates a bending angle for the steel plate at the heating point on the basis of an angle of intersection of the straight lines U, V; after obtaining a heating point, or a heating point and a bending angle, relative to a certain reference point, repeats the same steps as described above while bringing the contact points A, C on a reference point side, which have been used in the determination of the heating point, into contact with each other to use their contact point as a new reference point, thereby calculating respective heating points, or respective heating points and respective bending angles, along a specific line up to the end of the steel plate; and further having
a heating line determining unit which reads in data on the heating points calculated by the heating point determining unit; draws straight lines from a certain heating point on a certain line, as a starting point, to heating points on other lines on the basis of data on the respective heating points; examines the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if the degree of parallelism is within a predetermined range, performs grouping of the relevant heating points as the heating points of the same group; and connects the respective heating points of the same group by a straight line or a curve to determine a heating line; or
a heating line determining unit which reads in data on the heating points and bending angles calculated by the heating point determining unit; draws straight lines from a certain heating point on a certain line, as a starting point, to heating points on other lines on the basis of data on the respective heating points; examines the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if this degree of parallelism is within a predetermined range, performs grouping of the relevant heating points as the heating points of the same group; connects the respective heating points of the same group by a straight line or a curve to determine a heating line; and calculates the amounts of heating at the respective heating points on the basis of the data on the bending angles of the steel plate at the respective heating points; or
a heating line determining unit which reads in data on the heating points and bending angles calculated by the heating point determining unit; draws straight lines from a certain heating point on a certain line, as a starting point, to heating points on other lines on the basis of data on the respective heating points and bending angles; examines the degree of parallelism between each of the straight lines and a roller line involved during primary bending of the steel plate; if this degree of parallelism is within a predetermined range, and if the amounts of heating at the heating points determined by the bending angles of the steel plate at the respective heating points are equal to each other, performs grouping of the relevant heating points as the heating points of the same group; and connects the respective heating points of the same group by a straight line or a curve to determine a heating line.
According to the aspects 1) and 2) above, all the heating points, or heating points and bending angles, on a specific line of the steel plate can be determined automatically. Furthermore, heating lines and bending angles (amounts of heating) can be determined simultaneously. Besides, appropriate heating lines can be prepared automatically on the basis of information on the heating points. Consequently, automatic bending of a predetermined steel plate can be carried out by controlling the position of the heating unit of the high frequency heater on the basis of data on the heating lines.
FIGS. 4(a) and 4(b) show, by contour lines, the shapes of a steel plate before and after its heating along heating lines determined by the present invention. FIG. 4(a) represents the contour lines before heating, indicating the difference between the shape of the steel plate and the target shape as a difference in color. A blue portion at the center of the steel plate has a difference of 5 mm from the target shape, while a red portion at the end of the steel plate has a difference of 50 mm. These findings demonstrate that the farther from the center and the nearer the end, the greater a deviation from the target shape becomes. FIG. 4(b), on the other hand, represents the contour lines after heating the steel plate along the heating lines of the present invention. A look at this drawing will show that a blue portion widens, so that the shape approaches the target shape markedly. That is, sufficiently useful heating lines can be determined without the need to use a wooden pattern concerned with earlier technologies.
3) Dividing a curve of a target shape of a steel plate to be bent, into a plurality of successive segments; similarly dividing a curve of a measured shape of the steel plate into a plurality of successive segments in correspondence with the curve of the target shape; determining the number of a plurality of congruent isosceles triangles, which are connected together while sharing their equal sides, for each segment on the basis of the radius of a division of the curve in each segment of the target shape of the steel plate, the radius of a division of the curve in each segment of the measured shape of the steel plate, and a separately set bending angle of the steel plate so that when the division of the curve in each segment of the target shape of the steel plate is regarded as an arc, the arc in each segment of the target shape of the steel plate can be approximated by a fold line defined by the bases of the plural congruent isosceles triangles and that when the division of the curve in each segment of the measured shape of the steel plate is regarded as an arc, the arc in each segment of the measured shape of the steel plate can be approximated by a fold line defined by the bases of a plurality of other congruent isosceles triangles which are connected together while sharing their equal sides, the number of the latter isosceles triangles being the same as the number of the former isosceles triangles whose bases constitute the approximating fold line for the target shape; dividing the arc of the measured shape in each segment by the number of the isosceles triangles to form respective points on the arc; and using the respective points on the arc as heating points.
4) Having a heating point determining unit which reads in target shape data on a target shape of a steel plate to be bent, and steel plate shape measurement data obtained by measuring a surface shape of the steel plate; divides a curve of the target shape of the steel plate into a plurality of successive segments; similarly divides a curve of the measured shape of the steel plate into a plurality of successive segments in correspondence with the curve of the target shape; determines the number of a plurality of congruent isosceles triangles, which are connected together while sharing their equal sides, for each segment on the basis of the radius of a division of the curve in each segment of the target shape of the steel plate, the radius of a division of the curve in each segment of the measured shape of the steel plate, and a separately set bending angle of the steel plate so that when the division of the curve in each segment of the target shape of the steel plate is regarded as an arc, the arc in each segment of the target shape of the steel plate can be approximated by a fold line defined by the bases of the plural congruent isosceles triangles and that when the division of the curve in each segment of the measured shape of the steel plate is regarded as an arc, the arc in each segment of the measured shape of the steel plate can be approximated by a fold line defined by the bases of a plurality of other congruent isosceles triangles which are connected together while sharing their equal sides, the number of the latter isosceles triangles being the same as the number of the former isosceles triangles whose bases constitute the approximating fold line for the target shape; divides the arc of the measured shape in each segment by the number of the isosceles triangles to form respective points on the arc; and calculates the coordinates of the respective points as heating points.
According to the aspects 3) and 4), the deviation of the surface shape of the steel plate, the object to be processed, from the target shape is grasped as a geometrical problem mediated by the angle between the base of each isosceles triangle and the base of the adjacent isosceles triangle of the multiplicity of specific isosceles triangles. Thus, all the heating points on a specific line of the steel plate can be determined automatically.